Einstein

Sorry that should say XLR - RCA adapters. Thanks.

Although a lot of equipment having balanced outputs can tolerate having the inverted signal (pin 3 per the convention used in the USA and many other countries) grounded, some can't (see this thread for example, although it involved a solid state component), and personally it strikes me as being being poor practice at best. Also, the output impedances of the Einstein preamps are very low (especially for tube designs), which everything else being equal increases the likelihood of there being a problem.

There are three approaches that occur to me:

1)Cardas can supply adapters which leave pin 3 unconnected, although they are significantly more costly than standard adapters.

2)You could have a cable supplier custom make an adapter cable which leaves pin 3 unconnected.

3)You could purchase a Jensen transformer, such as their model PI2-XR (which is the same as the illustrated model PI2-XX except with RCA output connectors), and an additional set of cables if necessary. It would connect to the amp input with a very short length of RCA cable, and to the preamp with whatever length of XLR cable is necessary.

A transformer such as that one would in effect convert the unbalanced input of the amp to a balanced input, with the advantages that can potentially provide. Those would include reduced susceptibility to ground loop issues; reduced sensitivity to cable differences, especially in combination with the low output impedance and excellent drive capability of your preamp; perhaps lower noise levels, etc. A number of users here whom I consider to be highly credible and have very high quality systems have reported excellent results using Jensen transformers to adapt balanced to unbalanced connections, or vice versa, although there are also one or more highly credible members who assert that they introduce subtle sonic compromises.

Good luck. Regards,
-- Al

P.S: A fourth option, which I suspect would be an excellent choice although at a considerably higher price point, would be Steve McCormack's transformer-based SMc Audio Flex Connect. Note though that it provides a gain reduction of 12 db, which should be considered in the context of the gains, sensitivities, and source levels of your particular system.

Regards,
-- Al

A fifth option is to have the amplifier updated with a balanced input. Its not that hard (finding a place to put the connector is the hardest part), its cheap to do, does not change the character of the amp, does not use transformers, and does process both the inverted and non-inverted phases of the signal correctly.

We have been doing this update for years. But its not hard and any technician qualified to work on audio electronics could do it.

How it works: all tubes have two inputs, the grid and the cathode. Normally the cathode is ignored as an input. In this case we put it to work. While the result is differential, it is not truly balanced, but it does work quite well. The RCA input becomes pin 2 (signal) and pin 1 ground), pin 3 is the cathode input; a coupling cap is installed for this purpose. The input impedance is low but if the output impedance of the preamp is as low as touted, this is not and issue.

The problem you are up against is that normally balanced and single-ended connections really are not that compatible (one result of that is hum and buzz if there it trouble). But there are ways to make things work- we've been doing this longer than anyone else so we've learned a few tricks along the way.